▲ The closing benchmark Korea Composite Stock Price Index (KOSPI) is displayed on a screen inside the dealing room of Hana Bank in central Seoul on Sept. 14, 2026. (Yonhap)

(ATTN: ADDS bond yields in bottom)

SEOUL, Sept. 14 (Yonhap) -- Seoul stocks tumbled by more than 3 percent Monday as investors sold off tech-heavyweights on persisting geopolitical uncertainties and warnings from U.S. tech executives that the pace of artificial intelligence (AI) development may be too fast. The Korean won fell against the U.S. dollar.

After opening sharply lower, the benchmark Korea Composite Stock Price Index (KOSPI) closed down 225.54 points, or 3.26 percent, to 6,684.37.

Trade volume was light at 274.4 million shares worth 20.19 trillion won (US$14.93 billion). Losers outnumbered winners 561 to 308.

Retail investors were net buyers, snapping up 2.97 trillion won. Institutional and foreign investors offloaded a combined net 4.46 trillion won.

"The main factor that led the sharp decline was the controversy over the pace of AI development," said Lee Kyoung-min, an analyst from Daishin Securities.

An anticipated meeting expected to reopen transit in the Hormuz Strait was postponed, which led Brent crude, the international oil benchmark, to hover above US$108 per barrel, further cooling investor sentiment, the analyst added.

Over the weekend, Anthropic's co-founder Dario Amodei issued a proposal to slow down the advancement of AI technology to ensure public safety, of which followed a rare show of unity from other AI executives from the United States.

In Seoul, most market heavyweights ended lower.

Top-cap Samsung Electronics shed 4.05 percent to 249,000 won, and rival SK hynix retreated 6.35 percent to 1,697,000 won.

Battery maker LG Energy Solution dipped 2.36 percent to 351,500 won, carmaker Hyundai Motor slid 2.88 percent to 371,500 won, and defense giant Hanwha Aerospace jumped 5.18 percent to 1,137,000 won.

Financial stocks strengthened on anticipation that the central banks from South Korea and the U.S. will maintain a monetary tightening stance for a longer-than-expected period.

KB Financial added 2.08 percent to 181,600 won, and Shinhan Holdings inched up 1.51 percent to 114,600 won.

The Korean won was quoted at 1,347.3 won against the U.S. dollar, down 1.4 won from the close of the previous stock trading session.

Bond prices, which move inversely to yields, closed lower. The yield on three-year Treasurys rose 1.1 basis points to 4.025 percent, and the return on the benchmark five-year government bonds added 1.2 basis points to 4.279 percent.

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